This invention relates to an improved method for manufacturing a semiconductor mask programmable ROM (read only memory) including a plurality of matrix-arranged insulated gate enhancement type field effect transistors (hereinafter referred to simply as IGFET's).
The ROM including a plurality of semiconductor elements, expecially matrix-arranged IGFET's, is already known through varieties of literature and their improvement appears in the U.S. application Ser. No. 616,626 filed by the same assignee with this application.
The ROM is usually composed of a plurality of matrix-arranged IGFET's T.sub.ij (i = 1, 2, . . . m; j = 1, 2, . . . , n) as shown in FIG. 1. In reading out information stored in memory cells from such ROM, the ROM is so operated that one of selective lines S.sub.1 to S.sub.M is given a selecting signal and the information in the memory cells appears at the output of data lines D1 to DN. The memory cells correspond to their respective IGFET's T.sub.ij, and the information in each memory cell is determined by whether its corresponding IGFET is allowed to conduct by the selective signal or not. Therefore, in order to complete the ROM by writing information in the semiconductor device, the IGFET's should be so constructed that only a predetermined IGFET among a number of IGFET's T.sub.ij in the semiconductor device can operate, remaining IGFET's being prevented from operation. There are generally two types of well-known devices as completed ROM's including IGFET's to operate as memory cell, which are produced in different ways.